Process of concentrating ores



4June 23, `1942. s. B. MccLUsKEY PROCESS OF CONCENTRATING ORES FiiedMarch 14, 1940 INVENTOR 709. )m

ATTORN EYS Patented June 23, 1942 UNITED STATES PATENT OFFICE 2,287,115PROCESS F CONCENTRATING ORES Sibley B. McCloskey, New York, N. Y.

Application March 14, 1940, Serial No. 323,851

Claims. (Cl. 209-441) My invention relates to the concentration of oresand more particularly to the separation of ores into a plurality offractions of different specific gravities upon concentrating devices,such as shaking tables, designed to use the specie gravity differentialof the fractions `to promote the separation, and in which the mineralgrains are substantially in physical contact with each other asdistinguished from free suspension in a fluid or emulsied medium ofintermediate specific gravity, as in the so-called sink and floatprocesses.

The invention is directed primarily to the separation of two or morevaluable minerals for separate subsequent treatmentin an appropriatemanner, as distinguished from the primary concentration where thevaluable mineral or minerals are separated from the worthless gangue.For example, when metallic gold is mixed with arsenopyrite in theprimary concentrate, refining of the gold is facilitated if it is firstsubstantially freed from the arsenopyrite, and .treatment of the latterproduct for the recovery of locked, intercrystallized, or encasedparticles of gold will be more economically preformed, and less subjectto loss, if all free gold is removed.

In the mechanical separation or concentration of minerals by any of thewell known gravity concentration methods, numerous practicaldifficulties are encountered, and a high degree of efficiency is rarelyattained.

In the operation of well known tables of the shaking type, such as theWiley, Deister, Overstrom, Butchart, etc., on which, in the finalseparatory, or cleaning stage, the mineral is extended over an inclinedplane, usually to a depth not greater than one grain, the line ofdemarca tion between the minerals of different specific gravity is notclearly defined, and it is therefore impossible to make a preciseseparation. This is due in part to the practical difficulties in the wayof securing uniformity of grain size in the initial table feed, whichresults in a classification according to size, and therefore permits thecoarser grains of one class to penetrate or overlay the adjoining zonethrough which travel the finer grains of the mineral next lower in thegravity scale. This difficulty extends equally to deeply bedded devices,sucl! as full-rifiied tables, jigs, etc.

This deficiency is ameliorated to some extent in practice by theseparation of a middling" fraction of mixed mineral grains, which iseither sent to other machines for further fractionation, or is returnedto join the feed to the same machine, thus constituting a continuouslycirculating middling or buier zone. But this method is laborious andexpensive. If some such method ls not practiced, the eciency of theseparation is impaired, and one'or another of the objectives is notattained; either an excessively diluted concentrate, or an inadequatelyimpoverished residue results.

The object of my invention is 'to improve the efficiency of theseparation of the fractions of different specific gravity.

In accordance with my invention, I introduce into the granulated body ofore, supplied to the concentrating device, an extraneous granularsubstance of specific gravity intermediate that of the fractions to beseparated to thereby separate these fractions on the concentratingdevice so that their marginal limits are spaced edgewise from each otherby the extraneous material. In other words, I introduce an artificialmiddling, providing a supplementary buffer zone between the orefractions on their discharge from the concentrating device. Thefractions thus separated may be readily diverted into diierentcontainers.

The essential qualities of the extraneous substance or agent to beemployed are: First, it must be a homogeneous, granular, materialcharacterized by a specific gravity intermediate between that of the twominerals, r the two groups of minerals, which it is desired to separate,and: second-it must be so prepared that the size'of the particlesapproximates the median grain size of the minerals under treatment.

The separating agent should also be insoluble in the liquid, if any,used in the concentrating operation, and should be either inert andcapable of being readily separated from the mineral fractions orcap'able of practical commercial use in the subsequent treatment ofthefractions.

Various considerations, such as the cost of the material, the quantitiesconsumed, the cost of recovery, its effect on subsequent processing, andthe character of the material under treatment, wlll govern the selectionof the medium for any specific application.

VSuitable materials for use as separating agents are metals, or naturalmineral compounds, or artificial alloys.

Because of their distinctive metallurglcalcharacteristics, high specificgravity, wide distribution, and relatively low cost, compounds of leadand iron will be most generally applicable.

In the application of my invention to the treat- `ment of gold, silveradplatinum ores, one suitable addition agent is lead oxide or litharge.

Lithargehas a speciiic'gravity of 9.0, exceeding that of any of thenatural constituents of the ole except native gold, silver, and metalsof the platinum group, and will therefore occupy the zone next to theprecious metals, when stratified according to gravity by the actionofthe concentrating machine.

Litharge is a useful reagent in the subsequent treatment of bothfractions of the concentrate. In smelting the selected concentratefraction, with which may be mixed gold precipitates derived from otherstages of the ore-treatment procedure, the litharge is a useful ux,effective in the elimination oi' other base metals, and producing, oncupellation, a dor bullion of exceptional purity and recovering the leadas litharge, which after granulation, will be suitable for re-use in theprocess. As the reject fraction from this stage of the process willinvariably contain gold, usually in intimate physical association withthe sulphides, it will be necessary to treat this product, inconjunction with concentrate produced in other stages of the treatment,by cyanidation. Litharge is likewise a' useful reagent at this stage,and in common practice it is frequently employed as such, beingeffective, in the treatment of sulphide ores by cyanidation, both as anaccelerant to the solution of gold, and as an agent to inhibit theformation of soluble sulphides, sulpho-salts, and other cyamide-solutionfouling compounds.

Lead sulphide, or in its natural form, galena, has a specific gravityoi' 7.5 which is greater than any of the minerals commonly associatedwith precious metals. It provides a useful iiuxing 1 constituent totheconcentrate of such metals,

and is recoverable from the residue by ilotation, or in smelting. 'I'henatural lead carbonate, cerussite, sp. gr. 6.5, may be used to replace,or to supplement the artificial oxide of lead, litharge, sp. gr. 9. Bothof these compounds are useful iluxing agents in the concentrate, and a1-though not recoverable from the tailing by notation,.are useful reagentsin cyanidation. Metallic lead, in granular form (sp. gr. ll) may be usedin commotion with litharge, to enhance the elcacy of the separation, andto replace the normal consumption of the latter, as the bulk of metalliclead introduced in this manner will, due to its higher gravity, andrelative uniformity of grain-size, be included in the concentratefraction, and therefore recovered as litharge.

Iron, its compounds and ferro-alloys, such as granular iron or steel inthe form of turnings, or lings, ferro-silicon or other ferro-alloys, orin the mineral form, magnetite, present a wide range in specificgravity, from 5.1 (magnetite) to 8.0 (steel), with a selection ofintermediate gravities in the alloys. Other than in specific gravity,these substances exhibit almost identical physical and chemicalcharacteristics, insofar as the application of my invention isconcerned. lAll are amenable to magnetic separation. or if this is noteconomically warranted, are free from objection in such subsequenttreatment as flotatio or cyanidation.

In order that my invention may be better understood, several examples ofthe practical application thereof will be described.

I.'T1jeatment of' gold ores associated with deleterious sulphides In thetreatment of gold ores it; is common esV Amilling practice to attempt torecover as muchas possible oi the gold in the free state at an earlystage of the treatment procedure, by a simple form of gravityconcentration on corduroy or blanket tables. Gold recovered in thismanner is usually accompanied by a relatively large proportion ofsulphides and granular gangue minerals. The gold may be separated bydirect amalgamation, but this involves the treatment of a relativelylarge bulk of concentrate, by a non-continuous and laborious procedure,entailing excessive labor, and the risk of theft. A preferred method,likewise in common practice, is to re-concentrate the material onshaking tables or jigs, producing a relatively small bulk ofconcentrate, irom which the gold may be conveniently recovered, eitherby amalgamation or by direct smeltng.

When, as is a common occurrence with gold ores, the simple sulphides areaccompaniedA by arsenopyrite, the separation of the gold is ren-` deredmore diicult. Arsenopyrite has a specific-` gravity approximating 6.0,While the more ame-.

nable sulphides, such as pyrite, marcasite, and pyrrhotite have specificgravities `approximating 5.0. 4.9, and 4.6 respectively. In there-concentration of a product containing these minerals, the specificgravity differential will cause the arsenopyrite to accompany the gold.Where it is least desired, while the other sulphides will be largelyrejected. The deleterious action'of ab. senopyrite is observed in thesubsequenttreatment of the concentrate. If amalgamationis resorted tosickening" and iiouring of mercury ensues, causing losses of bothmercury and gold. If direct smelting is resorted to, preliminarycalcination is advisable and the formation of an objectionable speiss isinevitable.

In accordance with my invention, a predetermined quantity of a suitableseparation agent, such as litharge, is mixed in a finely dividedgranular form with the finely divided granular primary ore concentrate.The mixture is then fed to a shaking table where the mixture isclassiiled into thin bands or zones o i minerals of diflitharge isdiverted with the valuable concentrate,`

the remainder going with the arsenopyrite.

The accompanying drawing shows one method of practicing my invention.

In the drawing:

Fig. 1 is a diagrammatic plan view of the apparatus used, showing thecourse of the ore and the separating agent -and the distribution of theproducts on the cleaning area of the table;

Fig. 2A-is an end view of the table showing, at the point of thedischarge of the concentrate, the conventional practice of separatingtwo minerals, and,

, Fig. 2B Ais a view like that of'Fig. 2A, but show ing the practice ofmy invention. i

The invention, as shown, is carried out upon a table i of the shakingtype, of which the Wiley table is a well known example, on which thefinal separation is effected on a substantially plane cordance with myinvention the two concentrate .As shown (in an exaggerated way) inFigs.'2A

and 2B, the table has a slight inclination from the horizontal in alateral direction. The table is provided with'longitudinal rilllesforming shallow grooves tapering to nothing at the concentrate end, soas to form channels of diminishing depth. These channels terminate on aline extending diagonally across the table, as shown.

The ground mineral to be concentrated is sup plied to the table I from astorage vessel -6, through a conduit 'I controlled by a valve 8 andleading to a mixer 9. The ground separating agent is supplied from a.storage hopper IIJ through a feeder II to the mixer 9. From the mixer 9,the mixture of mineral and separating agent is delivered through conduitI2 to feed launder I3 from which it is delivered to the upper edge ofthe riffled portion of the table.

A launder I4 provides a supply of wash water for the table. Theseparated fractions of the concentrate are delivered to containers I5and I6 respectively. The tailing or gangue minerals, are discharged intothe launder I'I.

In operation, the water borne mineral mixture Il ows across the table,Vthe concentrate contain ing all of the minerals of high specificgravity passing into the channels 5, while the gangue minerals ofrelatively low'specic gravity overl flow into the tailings launder Il.

The longitudinal shaking imparted to the table causes the grains ofconcentrate to travel along the channels towards the smooth unriiiledportion of the table. l

After emerging from the riled section, the mineral grains are caused toextend over the plane surface of the unriilled area to a depth ofapproximately one grain. `The direction of travel of the mineral is theresultant of two forces, the table mechanism impelling -the minerallongitudinally while the iiow of the wash water tends to carry itlaterally. The travel of the mineral particles or grains depends uponboth their specific gravities and their sizes. The result is a gradualclassification; so that when the particles or grains reach theconcentrate discharge end of the table, they are arranged in hands orzones of different specific gravities. The band or zone of highestspecic gravity will be nearest the upper edge of the table, and thesucceeding bands or zones towards the lower edge of the table will be ofsuccessively lower specific gravities. The efliciency of the separationis aiected by variation in the size of the particles or grains, sincethe coarser grains of higher specic gravity tend to penetrate the uppersection of the zone of next lower speciiic gravity containing thesmaller grains o that fraction.

Figs. 2A and 2B show the arrangement of the mineral grains of theconcentrate at the time of their discharge from the` table. The grainsof high specific gravity are illustrated by black circles, the grains oflow specific gravity -by white circles. The grains of the separatingagent are illustrated by shaded circles. the size of the circlesrepresents the gradation in the size of the grains. As shown in Fig.`2A, where no separating agent is used, the larger particles of theconcentrate fraction of high specinc gravity are mixed with the smallerparticles of the concentrate fraction of low speciflc gravity. When,however, a separating agent is used in acfractions are separatedentirely from each other by the said agent. The smaller. grains of theagent are mixed 'and delivered to the container I5 with the largergrains ofy the concentrate fractionzof higher specic gravity, while thelarger grains of theV agent aremixed and delivered to the container I6with the concentrate fraction olf lower specic gravity.

. The introduction of a separating agent of intermediatespecic gravityserves to widen the zone separating'the two :minerals which it'isdesired'to separate, and thus makes it possible to eect a cleancut'between them. It-is obvious that portionsof the agent added will belincluded in both vfractions, and the nature of this agent musttherefore be determined by its eiect on subsequent treatment of theproducts, or the ease with which it may -be reclaimed.

In the concentration of gold orcs containing arsenopyrite with lithargeas a separating agent, the upper zone will contain the selectedconcentrate fraction and this will be separated by the lithargejfrom theconcentrate fraction containing the arsenopyrite. The arsenopyritewill'be substantially excluded from the selected fraction by thelitharge. V

In thetreatment of certain arsenical ores, it is occasionally necessary.to resort' to calcination prior to cyanidation. In such a case .thepresence of lead inthe roaster-feed is undesirable,

The gradation in and in the practice of my invention on such an ore,another addition agent should be substituted for litharge. Similarly, incertain applications, economic or other considerations may preclude theemployment of 'direct smelting and cupellation, and necessitate recoveryof the gold by amalgamation.' In this, as in the" preceding case, theuse`of litharge is fundesirable. In both instances, substitute additionagents are avail-Y Likewise stainless steel may be used.

II.-Trea1ment of ores of the platinum groupv metals Another applicationof my invention will be in the treatment of ores of the platinum groupmetals.v In certainoccurrences, these ores in clude the metals both inthe free and the alloyed state, and in intimate physical associationwith sulphides. In the treatment of these ores it is desirable to obtainas much metal as possible in the free state; as, in that case, thesubsequent rening process is,l simpler, and the value more promptly andeconomically realized. The sulphides must be subjected to a laborious,complex, and expensive procedure for the recovery of the metals,realization on which is both decreased and deferred. In order, however,to adequately concentrate the free-metal into the rst class, orfraction, the initial concentrate must be reconcentrated. Under currentmethods, a. .considerable percentage of the free metal inevitably findsits way into the sulphide fraction, with consequent' economic losses.

The sulphidesusually accompanying this type of ore are pentlandite (sp.gr. 4.6-5.0), chalcopyrite (sp.'gr. 4.1-4.3), pyrite (sp. gr. L9-'5.1).

Ill-Separation of base metal oxides of moderate gravity diferenceCertain oxides which exhibit minor differences in specific gravity, andare of limited otative qualities, and which present seriousdifiiculties-to separation by ordinary gravity methods, may besuccessfully treated by my invention. An example of this is theassociation of tin and tungsten, occurring as cassiterite andwolframite. The specific gravity of the former approximates '1.0, thelatter 7.5. The separating agent in this case would be preferablfone ofthe ferro-alloys of intermediate specific gravity, such as a.ferrosilicon of sp. gr. 7.25. The agent can be recovered from bothfractions for re-circulation by magnetic separation.

My invention is adapted to deal with material of a size much -ner than4can be treated by the known sink and float processes.v Using a Wilfleytable of the kind described, mineral granules ranging between 200 mesh(74 microns) and 2 mm. Amay be effectively treated. Native gold as fineas 10 microns may be recovered, and large flakes of gold or fragments ortramp gangue up to '/4 inch do not derange the operation.

While I have described certain applications of my invention. and certainseparating agents to be used therein, it is to be understood that I amnot limited to these applications and agents.

Having described my invention, what I claim 1. The process ofconcentrating-ore to produce a plurality of fractions of differentspecific gravities which comprises mixing the ore in a nely dividedstate with a nely divided artificial middling of homogeneous, granularmaterial characterized by having a specific gravity intermediate thespecific gravities of said fractions, separating on a transverselyinclined, longitudinally reciprocated plane surface the mixture thusproduced to produce a thin surface layer on said plane surfacecomprising zones of material each lying on said plane surface andcontaining said fractions respectively and separated edgewise vby saidmiddling, and collecting separately from said surface the material ofAsaid zones.

2. The process of concentrating ore to produce a plurality Vof fractionsof different specific gravities which comprises mixing the ore in afinely divided state with a finely divided artificial middling'ofhomogeneous, granular material characterized by having a specific-gravity intermediate the specic gravities of said fractions and havinga grain size substantially the same as the median grain size of the ore,separating on a transversely inclined, longitudinallyreciprocated planesurface, in a surface layer the mixture thus produced to produce zonesof material in said surface layer containing said `fractionsrespectively and separated by said middling, and collecting the materialof said zones separately, the said zones each lying on gravities whichcomprises mixing the ore in a finely divided state with a finely dividedartificial middling of homogeneous, granular material characterized byhaving a specific .gravity intermediate the specific gravities of saidfractions and having. a grain size substantially the same as the mediangrain size of the ore, separating the mixture thus produced in a surfacelayer upon a plane surface of a. shaking table whose plane surface istransversely inclined t0 the horizontal and reciprocated longitudinallyto produce zones of material in said layer containing said fractionsrespectively and separated edgewise by a region containing only saidmiddling, and collecting the Amaterial of said zones separately, thesaidzones each lying on said plane surface.

4. The process of separating ore to Vproduce a plurality of fractions ofdifferent specific gravities which comprises mixing the ore in a finelydivided state with an inert finely divided water insoluble artificialmiddling of homogeneous, granular material adapted to be readilyseparated from the remainder of said fractions, having a specificgravity intermediate the specific gravities of said fractions and havinga grain size substantially the same as the median grain size of the ore,removing gangue minerals from the mixture thus produced, and separating,on an inclined, longitudinally-reciprocated plane surface the remainderof the mixture in a surface layer into zones in said layer containingsaid fractions respectively and separated edgewise by said middling, andcollecting the material of said zones separatedly, the said zones eachlying on said plane surface.

5. The process of separating ore containing a precious metal to producea plurality of fractions of different specific gravities which comprisesmixing the ore in a finely divided state with a nely divided waterinsoluble artificial middling of homogeneous granular material of thekind which is useful as a flux for the elimination of base metals uponthe smelting of one of said fractions, which have a specific gravityintermediate the specific gravities of said fractions and having a grainsize substantially the same as the median grain size of the ore,removing gangue minerals from the mixture thus produced, and separating,on an inclined, longitudinally-reciprocated plane surface, the remainderof the mixture into a thin surface layer comprising zones containingsaid fractions respectively and separated by said middling, andcollecting the material of said zones separately, the said zones eachlying on said plane surface.

6. The process of separating ore containing gold associated witharsenopyrite to produce fractions containing the gold and arsenopyriterespectively which comprises mixing the ore in a finely divided statewith a finely divided water insoluble artificial middling of homogeneousgranular material of the kind which is useful as a flux for theelimination of base metals upon the smelting of one of said fractionsand which have a specific gravity intermediate the specific gravities ofthe gold and arsenopyrite and a gram size substantially the same as themedian grain size of the ore, separating the mixture thus produced in athin surface layer on a plane surface of a shaking table whose planesurface is transversely inclined to the horizontal and reciprocatedlongitudinally to produce separate fractions of gold and arsenopyriterespectively arranged in zones in said layer separated edgewise by saidmiddling, and 'separately collecting the material from said zones, thesaid zones each lying on said plane surface.

'LThe process of separating ore containing gold associated witharsenopyrite to produce fractions containing the gold and arsenopyriterespectively which comprises mixing the ore in a nely divided state witha nely divided water insoluble artificial middling of homogeneousgranular material selected from the group of materials consisting oflead and those compounds thereof which act as an accelerant to thesolution of the gold in cyanidation and which have a specific gravityintermediate the specific gravities of the gold and arsenopyrite and agrain size substantially the same as the median grain size of the ore,separating the mixture thus produced in a surface layer on a planesurface of a shaking table whose plane surface is transversely inclinedto the horizontal and reciprocated longitudinally to .produceseparatefractions of gold and arsenopyrite respectively arranged in zones insaid layer separated by said middling, and separately collecting thematerial from said zones, the said zones each lying on said planesurface.

8. The process of separating ore containing gold associated witharsenopyrite to produce fractions containing the gold .and arsenopyriterespectively which comprises mixing the ore in a. finely divided statewith a finely divided water insoluble `artificial middling ofhomogeneous granular material selected from the group of materialsconsisting f lead and those compounds thereof which act to inhibit theformation of cyanide solution fouling compounds and which have aspecific gravity intermediate the specific gravities of the gold andarsenopyrite and a grain size substantially the same as the median grainsize of the ore, separating the mixture thus produced in a surface layeron a shaking plane surface of a table whose plane surface istransversely inclined to the horizontal and reciprocated longitudinallyto produce separate fractions of gold and arsenopyrite respectivelyarranged in zones in said layer separated by said middling, andseparately'collecting the material from said zones, the said zones eachlying on said plane surface.

9. The process of separating ore containing gold associated witharsenopyrite to produce fractions containing the gold and arsenopyriterespectively which comprises mixing the ore in a nely divided state witha finely divided homogeneous metallic artificial middling having aspecific gravity intermediate the specific gravities of the goldandarsenopyrite and a. grain size substantially the same as the mediangrain size of the ore, separating the mixture thus produced in a surfacelayer on a plane surface of a shaking table Whose plane surface istransversely inclined to the horizontal and reciprocated longitudinallyto produce separate fractions of gold and arsenopyrite respectivelyarranged in zones in said layer separated by said middling, andseparately collecting the material from said zones, the said zones eachlying on said plane surface.

10, The process of separating ore containing gold associated witharsenopyrite to produce fractions containing the gold and arsenopyriterespectively which comprises mixing the ore in a finely.. divided statewith litharge finely divided to a grain size substantially the same asthe median grain size of the ore, removing gangue minerals from themixture, separating on 9, plane surface of a shaking table the remainderof the mixture to produce separate fractions of gold and arsenopyritearranged in zones in said layer separated edgewise by the litharge. andseparately collecting the material from said zones.

11. The process of separating ore containing a precious metal associatedwith a deleterious mineral and gangue minerals of lower specic gravity`than said deleterious mineral to produce fractions containing saidmetal and said deleterious mineral respectively which comprises mixing aprimary concentrate of the ore in a finely divided state with a finelydivided water insoluble artificial middlingl of homogeneous, granularmaterial having a'specic gravity intermediate the specific gravities ofthe metal and the deleterious mineral and having a grain sizesubstantially the same as the median grain size of the ore, removingsaid gangue minerals from the mixture. and separating the remainder ofthe mixture in a thin surface layer on a plane surface of a shakingtable whose pla-ne surface is transversely inclined to the horizontaland reciprocated longitudinally into separate fractions of metal anddeleterious mineral arranged in -thin zones of said layer separatededgewise by said middling, the said zones each lying on said planesurface.

i2. The process of separating ore containing a precious metal associatedwith a. deleterious mineral and gangue minerals of lower specificgravity than said deleterious mineral to produce fractions -containingsaid metal and said delemixing a primary concentrate o! the ore` in a.nely divided state with an artificial middling consisting ofhomogeneous, granular, nely divided metallic compound having a specicgravity intermediate the specific gravities of the metal and thedeleterious mineral and having a grain size substantially the same asthe median grain size of the ore, removing said gangue minerals from themixture, and separating the remainder of the mixture in a thin surfacelayer on a shaking plane surface of a table whose plane surfaceistransversely inclined to'the horizontal and reciprocated longitudinallyinto separate fractions of metal and deleterious mineral arranged inthin zones of said layer separated edgewise by said metallic compound,the said zones each lying on said plane surface.

13. The process of concentrating ore to produce a plurality of fractionsof different specific gravities which comprises mixing the ore in thefinely divided state with a nely divided artificial middling ofhomogeneous, granular material having a specific gravity intermediatethe specific gravities of said fractions, subjecting the mixture on aninclined plane surface simultaneously to agitation by longitudinalrecprocation of said surface and to the force of a stream of fluidacting in a direction parallel to said inclined plane surface toseparate said mixture into a thin layer on said plane surface consistingof zones containing respectively said fractions separated by athin-layer of said middling, the said zones each lying on said planesurface.

14. The process of concentrating ore to produce a plurality of fractionsof different specific gravities which comprises mixing the ore in afinely divided state withanely divided articial middling of homogeneous,granular material having a specific gravity intermediate the speciiicgravities of said fractions, subjecting said mixture to agitation on aninclined plane surface to separate said mixture into a layer on saidsurface having a depth substantially of `one grain and consisting ofzones of substantially one grain depth containing respectively saidfractions separated edgewise from each other by a. zone havingsubstantially one grain depth of said middling.

A 15. The process of concentrating ore containing a precious metal ofone speciiic gravity associated with deleterious minerals of differentspecific gravity tc produce fractions of said metal and said deleteriousmineral respectively which .comprises mixing a primary concentrate of'the ore in a nely divided state with a nely divided water insolubleartificial middlng of homogeneous granular material having a speciiicgravity intermediate the spqeciic gravities of said fractions and havinga grain size substantially the same as the median grain size of saidfinely divided ore, feeding said mixture on to an inclined surfaceundergoing agitation and subjecting said mixture on said surface to theaction of said agitation and to the force of a stream of liquid actingin a direction parallel to said inclined surface whereby the resultantof all forces acting on said mixture. will separate said mixture on aplane portion of said surface into a thin layer consisting of zones eachlying on said surface and containing respectively the fractionsseparated edgewise from each other by a zone consisting solely of saidmiddling.

SIBLEY B. MCCLUSKEY.

CERTIFICATE OF CORRECTION.

Patent Na. 2,287,115. June 25, 191m.

SIBLEY B. MOCLUSKEY.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Pagej,first column, lines h6 and 14T, and second column, line 50, claims 8 andl2 respectively, fox` "slnking plane surface of a table read --planesurface of a shaking tab1e and that the said Letters Patent should beread with` this correction therein that the same may conform tothe'record of the case in the Patent Office..

Signed and sealed this day of August, A. D. 1911.2.

Henry Van Arsdale Acting Commis sioner of Patents. (Seal)

